Thursday, January 04, 2007

Unit Testing with JUnit 4.0

JUnit 4 introduces a completely different API to the older versions. JUnit 4 uses Java 5 annotations to describe tests instead of using inheritence. It introduces more flexible initialization and cleanup, timeouts, and parameterized test cases. This post describes the new features in JUnit 4, and in the end, I show a basic example that tests the java.util.Stack class.

The tests: Unlike in JUnit 3.x you don't have to extend TestCase to implement tests. A simple Java class can be used as a TestCase. The test methods have to be simply annotated with org.junit.Test annotation as shown below

Using Assert Methods: In JUnit 4 test classes do not inherit from TestCase, as a result, the Assert methods are not available to the test classes. In order to use the Assert methods, you have to use either the prefixed syntax (Assert.assertEquals()) or, use a static import for the Assert class.

import static org.junit.Assert.*;

Now the assert methods may be used directly as done with the previous versions of JUnit.

Changes in Assert Methods: The new assertEquals methods use Autoboxing, and hence all the assertEquals(primitive, primitive) methods will be tested as assertEquals(Object, Object). This may lead to some interesting results. For example autoboxing will convert all numbers to the Integer class, so an Integer(10) may not be equal to Long(10). This has to be considered when writing tests for arithmetic methods. For example, the following Calc class and it's corresponding test CalcTest will give you an error.

This is due to autoboxing. By default all the integers are cast to Integer, but we were expecting long here. Hence the error. In order to overcome this problem, it is better if you type cast the first parameter in the assertEquals to the appropriate return type for the tested method as follows

Setup and TearDown: You need not have to create setup and teardown methods for setup and teardown. The @Before, @After and @BeforeClass, @AfterClass annotations are used for implementing setup and teardown operations. The @Before and @BeforeClass methods are run before running the tests. The @After and @AfterClass methods are run after the tests are run. The only difference being that the @Before and @After can be used for multiple methods in a class, but the @BeforeClass and @AfterClass can be used only once per class.

Parameterized Tests: JUnit 4 comes with another special runner: Parameterized, which allows you to run the same test with different data. For example, in the the following peice of code will imply that the tests will run four times, with the parameter "number" changed each time to the value in the array.

Have a public static method that returns a Collection for data. Each element of the collection must be an Array of the various paramters used for the test.

You will also need a public constructor that uses the parameters

Test Suites: In JUnit 3.8 you had to add a suite() method to your classes, to run all tests as a suite. With JUnit 4 you use annotations instead. To run the CalculatorTest and SquareTest you write an empty class with @RunWith and @Suite annotations.

8 comments:

Thanks for this post! It was of great help putting together a "data driven" suite for JUnit 4.0.

One question though: in the output reports from the tests, I only get testNumber[0], testNumber[1], testNumber[2], testNumber[3]. Would it be possible to get the input parameters as names for the test in the report?